Hot cathode electron discharge tube



Dec. 18, 1934. H. M. FREEMAN El AL 1,985,027

HOT CATHODE ELECTRON DISCHARGE TUBE 7 Original Filed Jan. 8, 1925 NV E NTO R5 flae/f/YF/eemn 5 M/hce 6 We 43.

ATTORN EY WITNESSES Z Patented Dec. 18, 1934 UNITED STATES PATENT OFFICE HOT CATHODE ELECTRON DISCHARGE TUBE Original application January 8, 1923, Serial No.

811,263. Patent No. 1933.

1,909,051, dated May 18,

Divided and this application July 8,

1928, Serial No. 120,583

This invention relates to hot-cathode electron discharge tubes and has particular relation to grid-controlled discharge tubes in which the electron-emitting cathode is heated from a source of alternating or fluctuating current and is so arranged as to substantially reduce or eliminate the undesirable eflects of the variations of the heating current on the electron discharge which is intended to be controlled.

Various arrangements for securing the foregoing eiiect have been disclosed in our copending application, Serial No. 611,263, filed January 8, 1923, Patent No. 1,909,051, May 16, 1933 of which the present application is a division.

Among the objects of the invention is the provision of an improved triode in which the cathode element is arranged to be heated with alternating or fluctuating current and is pro vided with a special auxiliary electrode so arranged around the heated cathode element as to substantially eliminate the magnetic and other eifects of the fluctuating current upon the part of the electron-discharge path whichis intended to be controlled.

In accordance with the invention, the foregoing results are obtained by providing, in the space between the heated cathode element and the grid which is intended to control the discharge i'rom the cathode element to the plate of the tube, an auxiliary grid electrode which is maintained at a predetermined potential with respect to the cathode so that a screen is provided against the effect of the current variations on the space exteriorly of the auxiliary electrode. In other words, the improved tube is so arranged that the auxiliary electrode which surrounds the hot electron emitter proper, functions as it if were an equi-potential cathode surface so that the control grid may be applied for controlling the discharge between the outer surface of said auxiliary electrode and the plate, as in an ordinary type of three-electrode tubes.

The invention will be best understood from the accompanying drawing, the single iigure'of which is an enlarged view, partially in elevation and partially in section of an electron-discharge tube, combined with a diagrammatic view of the associated circuits, embodying the invention.

Referring to the drawing, an electron-discharge tube comprises an evacuated envelope 1, of glass or the like, having a re-entrant stem 2 terminating in a press 3. A plurality of leadin-wires 5 to 10 are fused into the press and serve to support the electrode assembly 11 constituting the discharge path within the tube.

The electrode assembly comprises an elongated, centrally-disposed cathode member 12 which is surrounded, in succession, by an auxiliary grid or cathode-control electrode 13, the main control grid 14 and a tubular plate 15.

The cathode member 12 comprises a U-shaped' heater wire 17 having its ends connected to the lead-in wires '7 and 8 through which the heater wire is energized, and a tubular metal casing 18 surrounding the heater wire, the outer surface of which constitutes the electron-emitting cathode element of the tube. The cathodeemitting casing 18 is preferably insulated from the heater element 17 so as to eliminate, as much as possible, the magnetic and other effects of the alternating current utilized to energize the heater wire upon the electron flow from the cathode surface. The heat transmission from the heater wire to the casing may take place through radiation or through conduction, the space between the casing and the heater wire being, in the latter case, filled with a suitable refractory body, zircon for instance.

A carrier rod 19, extending from lead-in wire 5 in the press, serves to support the upper end of the cathode member -12 and to make the connection with the casing 18 constituting the oathode element thereof. The main control grid 14 and the tubular plate 15, which are arranged concentrically with the outer surface of the cathode member 12, are supported on suitable extensions from the lead-in wires 9 and 10 and may be constructed in any approved manner.

In a tube having a cathode construction, as described above, the magnetic field induced by the current flowing in the two parallel, closelydisposed sides of the heater wire 17 will be reduced to a very small value.

However, under certain conditions, it is desirable to further reduce the remaining disturbing effects of the fluctuations of the heating current in the cathode and to this end an auxiliary cathode-control grid .13 is interposed in the space between the main control gridand the outer surface of the cathode element 18.. The additional auxiliary grid element 13 is maintained at a positive potential with respect to the outer surface of the cathode element and acts like an electrostatic screen tending to suppress any control action that the alternating currents in the cathode member may tend to exercise upon the flow of electrons towards the plate. when the auxiliary grid is arranged and connected with respect to the cathode as described, it forms in effect an artificial cathode, insofar as the electron flow in the space from the outer surface of the auxiliary grid to the anode is concerned, the main control grid 14 serving to control this electron flow.

Any of the circuits familiar to those skilled in the art may be applied to the tube construction as shown above, the only difference being' that the cathode may be excited by alternating current without incurring the usual undesirable controlling effects incident to such excitation. A high frequency signalling system associated with the tube embodying the invention is shown in the drawing. The terminal leads 7 and 8 of the heater wire 17 are energized from a source of alternating current, such as a transformer 21.

A battery 22, or similar source of direct-current potential, -is connected between the outer cathode element 18 and the cathode-control or auxiliary grid 13 'to maintain the same at a positive potential with respect to the outer cathode surface, asexplained above. Input conductors 23, from a source of incoming signals (not shown) may be connected to the input terminals of the tube in the usual manner, for instance, by connecting one conductor to the main control grid 14 and the other conductor to the equi-potential cathode surface 18. The output circuit of the tube is shown including a detector or other load device 24 and a serially-connected source of plate energy 25.

The idea underlying the invention, to wit, the use of a cathode screen for the elimination of the undesirable effects of the variationsof the cathode heating current upon the part of the electron discharge path which is intended to be externally controlled, is not limited to the specific details of the circuit and construction illustrated and described hereinabove, but may be utilized in numerous other combinations and arrangements that will readily suggest themselves to those skilled in the art. For instance, instead of utilizing the cathode construction in which the electron-emitting element is constituted by a tubular member surrounding and insulated from the heater element, the electron source may be in the shape of an ordinary filament, such asis used in connection with directcurrent-excited cathodes.

In all cases, the essential feature of the invention is the reduction of undesirable effect of the variations in the exciting current on the electron flow by screening the electron-emittingelement with an auxiliary electrode member which acts as if it were the electron source, although the real source of electrons is distinct and separated therefrom.

The term grid in the specification and the appended claims is intended to designate broadly any electrode structure exercising a controlling eifect similar to the grids generally utilized in radio receiving tubes and the like.

It is accordingly desired that the appended claims shall be construed to cover all such modifications as fall within the spirit of the invention.

We claim as our invention:

1. In a high-frequency signalling system comprising a space-current discharge tube in which a control electrode is utilized to control an elec-- tron current flowing from a cathode to an anode and in which the cathode is maintained in an electron-emitting. state by heating the same with alternating current, anauxiliary electrode disposed between the' control electrode and the electron-emitting surface of the cathode and means for controlling the potential of said control electrode relative to said auxiliary electrode.

2. In a hot-cathode electron-discharge-tube device, an evacuated vessel, an anode and a cathode disposed in spaced relation within said vessel, means for supplying periodic current for heating said-cathode to cause electron emission therefrom, an auxiliary electrode interposed in the space between the electron-emitting surface of said cathode and said anode, means for maintaining said auxiliary electrode at a constant potential relative to said cathode, and an additional auxiliary electrode disposed in the space between said first auxiliary electrode and said anode and means for controlling the relative potential of said auxiliary electrodes.

3. In an electron-discharge-tube device, an evacuated tube, a cathode and an anode constituting an electron discharge path within said tube, exciting means for producing electron emission from said cathode, said exciting means tending to exert a periodic controlling action upon the electron flow in the space between said cathode and said anode, an auxiliary electrode interposed between the cathode and the anode and arranged and maintained at such a potential relative to said cathode as to permit the passage of electrons from said cathode to said anode, but to restrict the controlling action of said exciting means to the space between said cathode and said auxiliary electrode, and means for exerting an independent controlling action on the flow of electrons in the space between said auxiliary electrode and said anode.

4. In an electron-discharge-tube device, an evacuated vessel, a longitudinal cathode element, a tubular anode surrounding said cathode element, means for supplying said cathode with periodic current for heatingthe same to a temperature at which it emits electrons flowing towards said anode, a screen electrode interposed between said cathode and said anode, and maintained at such a potential relative thereto as to restrict the influence of the variations of the heating current to the space between said cathode and said screen electrode while permitting the flow of electrons to said anode, and an additional electrode for individually controlling the flow of electrons in the space between said screen electrode and said anode.

5. In an electron-dischar'ge-tube device, an evacuated vessel, concentrically-arranged cathode and anode elements in'said vessel, an auxiliary electrode interposed between said anode and cathode elements and separating the space between the same into two regions, means for heating said cathode by an alternating current to produce electron emission therefrom, said auxiliary electrode being maintained at a positive potential with respect to said cathode, and means for controlling the electron discharge in the region between said screen electrode and aid anode. g

6. In an electron-discharge-tube device, an evacuated vessel, an elongated cathode member, a tubular plate surrounding said cathode member, means for supplying said cathode element with an alternating heating current for securing a flow of electrons from said cathode member to said plate, a tubular grid electrode surrounding said cathode member and dividing the space between said cathode and plate into two con- 10 centric regions, means for maintaining said grid electrode at such a positive potential with respect to said cathode as to substantially screen the influence of the variations of the heating current from the region between said grid electrode and said plate, and an auxiliary tubular control electrode surrounding said first-mentioned grid electrode to control the electron discharge in the region adjacent to said plate.

HUBERT M. FREEMAN. WALLACE G. WADE. 

